1. Technical Field
Embodiments of the present invention relate to the field of piezo-electric transducers in ink jet printers.
2. Description of the Related Arts
There are ink jet printers in the art. FIG. 1A illustrates a common mechanical structure of a length expander piezo-electric ink jet according to the prior art. As illustrated, a piezo-electric driver (e.g., transducer A 105, transducer B 110, transducer C 115, transducer D 120, transducer E 125, transducer F 130, and transducer G 135) exists for each separate channel. The transducers are not mechanically isolated from each other. Each of the transducers is in communication with the same mechanical transducer support structure 100. When a voltage is applied to a transducer or an existing voltage is rapidly changed, the transducer “fires” (i.e., rapidly elongates), extending in a direction opposite the mechanical transducer support structure 100.
When one of the transducers is fired, its motion is coupled mechanically to all of the other transducers. This results in “structural crosstalk.” Crosstalk is a change in velocity and volume of an ejected drop of ink caused by the simultaneous (or prior firing) firing of one or more other channels. Crosstalk can result in degradation of print quality. The changes in drop velocity and size can be positive or negative. However, the crosstalk between adjacent channels is often negative.
FIG. 1B illustrates a common mechanical structure of a length expander piezo-electric ink jet after a transducer is fired according to the prior art. The reason for negative crosstalk between adjacent channels is illustrated by considering the common mechanical “rear mount” (i.e., the mechanical transducer support structure 100) for the transducers as a beam. When one transducer is fired, it extends in length to push against an ink chamber which reduces the volume of the chamber in order to expel a drop of ink. This length extension also results in a reaction force in the opposite direction on the mounting beam. The beam is therefore pushed away from the ink chambers and thus the adjacent transducers are also pulled away from their ink chambers as shown in FIG. 1B.
As illustrated, when transducer D 120 is fired, it expands in length and its lower end is initially displaced in a downward direction to drive an ink drop out of the chamber. The other end, however, is displaced in the opposite direction, pushing against the mechanical transducer support structure 100, causing it to deform. This deformation is propagated as a mechanical wave in the structure and the structure undergoes a damped vibration. The mechanical transducer support structure 100 necessarily deforms, as it is not possible to make it completely rigid. The adjacent transducers A 105, B 110, C 115, E 125, F 130, and G 135 are also pulled upward initially because they are also attached to the mechanical transducer support structure 100. If any of the adjacent transducers are fired at the same time as D 120, the initial upward motion will subtract from the firing motion, resulting in a smaller push on the chamber, resulting in a slower, smaller drop; thus, negative crosstalk. A similar explanation applies to the refill part of the drive pulse.
An additional deficiency results from use of the common support structure. The support structure is part of a housing connecting the beam on which the transducer is mounted to the fluid parts of the inkjet which, in turn, are connected to the other ends of the transducers. In general, the thermal coefficient of expansion of the transducers differs from that of the support structure. Temperature changes therefore can result in stresses which change the performance characteristics of the jets. These stresses and, consequently, the performance changes vary according to the location of a transducer in the array of transducers being fired.
Accordingly, current piezo-electric inkjet printing systems are deficient because the transducers are coupled to a common support structure, resulting in negative crosstalk between transducers. The common structure can also cause variations in performance due to temperature changes.